There was a Tesla battery teardown posted a while back where they weren't using properly isolated tools/equipment. This was from people who supposedly work on EVs for a living.

I'd be really nervous about letting someone work near 400V/1500A that wasn't trained to understand how to safely operate in that type of environment.

I don't mean "do it yourself" in terms of the actual working near 400 volts. I mean "do it yourself" in terms of diagnosis and "supervising" the logistics of a repair. If you need bodywork, Tesla could easily facilitate tracking down the parts and the bodywork/assembly procedures on their website. If your local mechanic isn't so search savvy, then the owner could have access to the same site to act as a facilitator. Heck, they could build a stripped-down project management for the repair project into such a site.

Isn't that the kind of problem that tends to short[sic] itself ;-)

1500 Amps???

Indeed. There's a crazy amount of current going through these things. Apparently the limit used to be 1200A, and beyond that, traditional fuses don't work well because the metal vaporizes and starts conducting electricity even after the fuse wire has melted. To get to 1500A they created a computer-controlled pyrotechnic fuse. That's what enabled the "ludicrous mode" that you can get on their high-end cars.

Good service overall is a tough problem, but ensuring adequate parts availability doesn't seem like a particularly difficult thing. Keep a small stock of every part at a warehouse somewhere, ship it out to shops that need them when they ask.

Reliably getting parts to a shop in days could be tough. Reliably doing it in weeks shouldn't be. That these repairs take so long tells me that they have no stock, and sit on their hands for a long time before making any.